#define  _CRT_SECURE_NO_WARNINGS
class Solution {
public:
    bool isUnique(string astr) {
        if (astr.size() > 26)return false;
        int bitmap = 0;
        for (int i = 0; i < astr.size(); i++)
        {
            if (bitmap & (1 << astr[i] - 'a'))return false;
            bitmap |= (1 << astr[i] - 'a');
        }
        return true;
    }
};